Thanks for reaching out! We are still in the process of writing documentation and this one is on our list.
createEdgeSprites() is a function that creates 4 sprites: leftEdge, rightEdge, bottomEdge, and topEdge that are placed at each edge just out of view. It puts them into a group called edges, which makes it easy to do something like characterSprite.bounceOff(edges) or characterSprite.collide(edges). These variables will autocomplete in text mode of Game Lab.
Here is an example: https://studio.code.org/projects/gamelab/nMHXNirEFnftt8o3tK3zVHLOoKeL2EIm-XPOxKuxZ_8